Most later-stage clinical trials are monitored for the possibility of
early stopping for efficacy or futility by a data and safety
monitoring board (DSMB), with interim analyses planned at either
fixed, predetermined analysis times or when specified proportions of
the total “statistical information” to be gained from the completed
trial have accrued[1]}. Ordinarily, at the time of an
interim analysis, the test statistic to be used for the final analysis
is computed based on the available data and compared to a suitable
stopping boundary constructed to preserve the overall operating
characteristics of the trial[2]}, [3]}.
